It is no exaggeration that miniaturization of a semiconductor integrated circuit pattern has been accomplished due to the progress of photolithography and peripheral techniques thereof. This photolithography includes two generally known main techniques. One is a technique on an exposure wavelength or a numerical aperture of a reduction projection exposure apparatus known as a stepper or a scanner. The other is a technique on resist characteristics such as printing resolution of a photoresist composition in which a mask pattern is printed by the aforementioned reduction projection exposure apparatus. These have improved processing accuracy of a semiconductor integrated circuit pattern by means of photolithography.
The wavelength of light sources used in the reduction projection exposure apparatus has been increasingly shortened in response to a demand for high resolution circuit patterns. In general, the g-line (436 nm) or i-line (365 nm) of a mercury lamp is used in the case of a resist resolution of about 0.5 μm or 0.30 to about 0.5 μm, respectively. The main spectra of the g-line and i-line are 436 nm and 365 nm, respectively. Also, a KrF excimer laser (248 nm) and an ArF excimer laser (193 nm) are used in the case of a resist resolution of 0.15 to about 0.30 μm, or about 0.15 μm or less, respectively. Furthermore, use of an F2 excimer laser (157 nm), an Ar2 excimer laser (126 nm), and EUV (extreme ultraviolet light, wavelength: 13 nm) is being investigated in order to further miniaturize a semiconductor integrated circuit pattern.
As far as a photoresist composition is concerned, the life of a photoresist for KrF in lithography using a KrF excimer laser is currently prolonged by combining this photoresist with an organic or inorganic anti-reflective film or by devising an exposure system, and the photoresist composition with an eye to about 110 nm, which is below λ/2, is being developed. Also, provision of a photoresist composition for ArF has been desired, which is preferable for the mass production of a prospective fine pattern with a node of about 90 nm or less in lithography using an ArF excimer laser. Furthermore, lithography using the aforementioned F2 excimer laser has drawn attention as a technique for processing a prospective fine pattern with a node of 65 nm or less, and a photoresist composition is being developed which is applicable to fine processing by lithography using an F2 excimer laser.
Since it is difficult for a conventional positive photoresist including an alkali soluble novolak resin and a quinone diazide group-containing compound as main components to achieve such a fine pattern, a photoresist applicable to a far-UV ray with a further shortened wavelength (200 to 300 nm); an excimer laser such as KrF, ArF, or F2; an electron beam; and X ray has been desired to be developed. As such a photoresist, a chemically amplified resist has drawn attention and is being actively developed, in which a catalytic reaction and a chain reaction due to an acid generated on exposure to radiation can be realized, the quantum yield is 1 or higher, and high resolution and sensitivity can be achieved.
A resin containing an acid dissociable, dissolution inhibiting group is mainly used in a positive chemically amplified resist.
Examples of an acid dissociable, dissolution inhibiting group used in the chemically amplified resist include an acetal group, a tertiary alkyl group such as a tert-butyl group, tert-butoxycarbonyl group, and tert-butoxycarbonylmethyl group as an acid dissociable, dissolution inhibiting group for a fluorinated alcohol as disclosed in the following non-patent references 1 to 3.
Also, as described in the following patent reference 1, a structural unit derived from a tertiary ester compound of (meth)acrylic acid, for example 2-alkyl-2-adamantyl (meth)acrylate, is generally used as a structural unit containing an acid dissociable, dissolution inhibiting group in a resin component of a conventional ArF resist composition. In the present specification, “acrylic acid” and “methacrylic acid” are collectively referred to as “(meth)acrylic acid”, “acrylic acid derivative” and “methacrylic acid derivative” are collectively referred to as “(meth)acrylic acid derivative”, and “acrylate” and “methacrylate” are collectively referred to as “(meth)acrylate”.
However, an acid dissociable, dissolution inhibiting group used in these chemically amplified resists disclosed in non-patent references 1 to 3 has a problem in terms of the improvement of resolution and the formation of a fine pattern with a good rectangularity because an alkali dissolution inhibiting effect in a unexposed part is insufficient (thickness loss occurs in a resist pattern). Provided that an introduction rate of an acid dissociable, dissolution inhibiting group is increased to improve an alkali dissolution inhibiting effect in a unexposed part, there is another problem in that the risk of defect is increased.
Also, as described in the patent reference 1, a compound forming a cyclic or linear tertiary alkyl ester with a carboxyl group of (meth)acrylic acid is well-known as a compound forming an acid dissociable, dissolution inhibiting group. However, there is a limitation to the number of types of an available acid generator. In other words, there is a problem of not working as a chemically amplified positive resist because an acid dissociable, dissolution inhibiting group is not dissociated unless an acid generator is used, in which acid strength of a generated acid is strong, for example an onium salt containing a fluorinated alkylsulfonic acid ion at an anion part. Also, there is another problem in that sensitivity is not sufficient when an acid generator is used, in which acid strength of a generated acid is weak. The improvement of these problems has highly been desired.
[Non-Patent Reference 1]
T. Hagiwara, S. Irie, T. Itani, Y. Kawaguchi, O. Yokokoji, S. Kodama, J. Photopolym. Sci. Technol. Vol. 16, Page 557, 2003
[Non-Patent Reference 2]
F. Houlihan, A. Romano, D. Rentkiewicz, R. Sakamuri, R. R. Dammel, W. Conley, G. Rich, D. Miller, L. Rhodes, J. McDaniels, C. Chang, J. Photopolym. Sci. Technol. Vol. 16, Page 581, 2003
[Non-Patent Reference 3]
Y. Kawaguchi, J. Irie, S. Kodama, S. Okada, Y. Takebe, I. Kaneko, O. Yokokoji, S. Ishikawa, S. Irie, T. Hagiwara, T. Itani, Proc. SPIE, Vol. 5039, Page 43, 2003
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. Hei10-161313